Earlier we said that the projection of the state vector onto one of
the perpendicular axes of its Hilbert Space shows the contribution of
that axes' eigenstate to the whole state. According to quantum
physics a quantum system can exist in a mix of all of its allowed
states simultaneously. This is the Principle of Superposition, and it
is key to the power of the quantum computer. While the physics of
superposition is not simple at all, mathematically it is not difficult
to characterize this kind of behavior.